Systems and methods for control of transmission and/or prime mover

ABSTRACT

Disclosed here are inventive systems and methods for a powertrain of an electric vehicle (EV). In some embodiments, said powertrain includes a continuously variable transmission (CVT) coupled to an electric drive motor, wherein a control system is configured to control the CVT and/or the drive motor to optimize various efficiencies associated with the EV and/or its subsystems. In one specific embodiment, the control system is configured to operate the EV in an economy mode. Operating in said mode, the control system simultaneously manages the CVT and the drive motor to optimize the range of the EV. The control system can be configured to manage the current provided to the drive motor, as well as adjust a transmission speed ratio of the CVT. Other modes of operation are also disclosed. The control system can be configured to manage the power to the drive motor and adjust the transmission speed ratio of the CVT taking into account battery voltage, throttle position, and transmission speed ratio, for example.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/285,463, filed May 22, 2014 and scheduled to issue on May 3, 2016 asU.S. Pat. No. 9,328,807, which is a continuation of U.S. applicationSer. No. 12/525,294, filed Jul. 30, 2009 and issued as U.S. Pat. No.8,738,255 on May 27, 2014, which is a national phase application ofInternational Application No. PCT/US08/052685, filed Jan. 31, 2008,which claims the benefit of: U.S. Provisional Patent Application No.60/887,767, filed Feb. 1, 2007; U.S. Provisional Patent Application No.60/895,713, filed Mar. 19, 2007; and U.S. Provisional Patent ApplicationNo. 60/914,633, filed Apr. 27, 2007. The disclosures of all of theabove-referenced prior applications, publications, and patents areconsidered part of the disclosure of this application, and areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to mechanical powertransmission, and more specifically to systems for and methods ofcontrol of continuously variable transmissions and electric drivemotors.

RELATED TECHNOLOGY

Electric vehicles are becoming more popular around the world as batteryprices decline and technology and performance advance. Factors such ashigh fuel costs and internal combustion engine emissions are makingelectric vehicles more attractive to customers looking for acost-effective commuting option. However, the performance and range of atypical electric vehicle is often inferior when compared to that ofcompetitive gasoline-powered vehicles. Additionally, manufacturer statedmaximum speed and range values are often based on idealized duty cyclesthat are not representative of real-world conditions.

There is a need for technology that can increase performance and rangeof electric vehicles to make them competitive with gasoline-poweredvehicles; hence, providing quiet, clean, and efficient transportationfor commuters worldwide. By way of example, as described herein below inrelation to inventive embodiments, integrating a continuously variabledrivetrain (for example, employing a continuously variable transmissionand suitable control strategies) in electric vehicles yields numerousadvantages.

SUMMARY OF THE INVENTION

The systems and methods described herein have several features, nosingle one of which is solely responsible for the overall desirableattributes. Without limiting the scope as expressed by the claims thatfollow, the more prominent features of certain embodiments of theinvention will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Inventive Embodiments,” one willunderstand how the features of the systems and methods provide severaladvantages over related traditional systems and methods.

One aspect of the invention concerns a drive system having a prime movercoupled to a continuously variable transmission (CVT). The drive systemincludes a control system operably coupled to the CVT, wherein thecontrol system is configured to manage power distribution to the primemover, and wherein the control system is further configured to adjust atransmission speed ratio of the CVT.

Another aspect of the invention is directed to a drive system having acontinuously variable transmission (CVT) and a control system coupled tothe CVT. The control system includes a mechanical actuator coupled tothe CVT, a controller configured to be in electrical communication withthe mechanical actuator (the controller configured to control themechanical actuator), a data display configured to be in electricalcommunication with the controller, and a plurality of sensors coupled tothe controller.

Yet another aspect of the invention is addressed to a control system foruse with a continuously variable transmission (CVT). The control systemhas a controller configured to provide a plurality of operating modesfor the CVT, said modes being selectable by a user of the CVT. Thecontrol system can further include an actuator motor coupled to the CVTand in electrical communication with the controller. In one embodiment,the control system also includes a drive motor coupled to the CVT and inelectrical communication with the controller. In one embodiment, thecontrol system includes an actuator position sensor coupled to theactuator motor and in electrical communication with the controller,wherein the actuator position sensor is configured to provide anindication of a transmission speed ratio of the CVT.

In one aspect the invention is concerned with a drive system having acontinuously variable transmission (CVT) housed in a wheel hub, a drivemotor operably coupled to the CVT and configured to provide power to theCVT, and an actuator motor coupled to the CVT and configured to adjust atransmission speed ratio of the CVT.

Yet a different aspect of the invention is directed to a control systemfor a drivetrain having a continuously variable transmission (CVT) and adrive motor. The control system includes a controller having amicrocontroller, a random access memory, and a flash memory; a powercontrol module configured to be in electrical communication with a powersource and the controller, the power control module adapted to regulatea voltage; and a communication interface operably coupled to the powercontrol module and the controller, the communication interfaceconfigured to connect to an external programming or data acquisitionhardware. The control system can also include a main drive moduleconfigured to communicate with the controller, the main drive modulefurther configured to modulate electrical power provided to the drivemotor; and an actuator control module configured to communicate with thecontroller, the actuator control module operably coupled to the CVT.

In one aspect, the invention is directed to a control system for adrivetrain having a continuously variable transmission (CVT), anactuator motor, and a drive motor. The control system includes atransmission controller module configured to communicate with theactuator motor, a drive motor controller module configured tocommunicate with the transmission controller module and the drive motor,and a throttle position sensor configured to communicate with thetransmission controller. The control system can additionally include abrake cut-off switch configured to communicate with the drive motorcontroller, a wheel speed sensor configured to communicate with thetransmission controller, and an actuator position sensor configured tocommunicate with the transmission controller.

In another aspect, the invention concerns a method of controlling adrivetrain of a vehicle having a continuously variable transmission(CVT) and a drive motor. The method includes the steps of sensing avehicle speed and a battery voltage, determining an optimum transmissionspeed ratio of the CVT based at least in part on the sensed vehiclespeed and battery voltage, and commanding a shift actuator of the CVTbased at least in part on the optimum transmission speed ratio.

Yet one more aspect of the invention is directed to a controller havinga controller housing, which controller housing exhibits an interiorcavity; a controller board assembly coupled to the controller housingand arranged in the interior cavity. In one embodiment, the controllerboard assembly includes a motor controller board and a transmissioncontroller board, which transmission controller board is configured tobe in electrical communication with the motor controller board.

Yet another aspect of the invention addresses a controller housinghaving a body with a generally rectangular-shaped interior cavityadapted to receive a controller board assembly. Said body includes, inone embodiment, a plurality of protrusions located on the interiorcavity, the protrusions configured to attach to the controller boardassembly. Said body can further be provided with a potting formed in theinterior cavity, the potting configured to enclose substantially thecontroller board assembly.

These and other improvements will become apparent to those skilled inthe art as they read the following detailed description and view theenclosed figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a drive system that can implement thecontrol systems and methods disclosed here.

FIG. 2 is a block diagram of one embodiment of a control system that canbe used with the drive system of FIG. 1.

FIG. 3 is a block diagram of a drive control system having an integratedcontroller.

FIG. 4 is a perspective view of a drive control system as implemented ina vehicle.

FIG. 5 is a second perspective view of the drive control system of FIG.4.

FIG. 6 is a perspective view of one embodiment of a user interfacedevice that can be used with the control system of FIG. 2.

FIG. 7 is a schematic block diagram of one embodiment of an integratedtransmission and drive motor controller that can be used with the drivesystem of FIG. 1.

FIG. 8 is a schematic block diagram of one embodiment of a transmissionand drive motor controller adapted to cooperate with a stand alone drivemotor controller.

FIG. 8A is a schematic block diagram of one embodiment of a CVTcontroller adapted to cooperate with a stand alone drive motorcontroller.

FIG. 9 is a chart showing a typical saw tooth vehicle acceleration thatcan be simulated by embodiments of the transmission and/or prime movercontrollers disclosed here.

FIG. 10 is a data table showing observed differences and advantagesobtained by using the transmission and/or prime mover controllersdisclosed here as compared to certain known fixed ratio drive systems.

FIG. 11 is a schematic diagram of one embodiment of a transmissionand/or prime mover control system according to inventive systems andmethods disclosed here.

FIG. 12 is a schematic diagram of a power control module that can beused with the control system of FIG. 11.

FIG. 13 is a schematic diagram of a universal serial bus interface thatcan be used with the control system of FIG. 11.

FIG. 14 is a schematic diagram of a test interface that can be used withthe control system of FIG. 11.

FIG. 15 is a schematic diagram of a controller that can be used with thecontrol system of FIG. 11.

FIG. 16 is a schematic diagram of a main drive module that can be usedwith the control system of FIG. 11.

FIG. 17 is a schematic diagram of a user interface module that can beused with the control system of FIG. 11.

FIG. 18 is a schematic diagram of a shift actuator control module thatcan be used with the control system of FIG. 11.

FIG. 19 is a schematic diagram of a serial peripheral interface that canbe used with the control system of FIG. 11.

FIG. 20 is a schematic diagram of a com interface module that can beused with the control system of FIG. 11.

FIG. 21 is a schematic diagram of a power monitor module that can beused with the control system of FIG. 11.

FIG. 22 is a block diagram of a control system that can be used with thedrive system of FIG. 1.

FIG. 23 is a block diagram of one embodiment of yet another controlsystem that can be used with the drive system of FIG. 1.

FIG. 24 is a block diagram of one embodiment of another control systemthat can be used with the drive system of FIG. 1.

FIG. 25 is a block diagram of one embodiment of yet another controlsystem that can be used with the drive system of FIG. 1.

FIG. 25 A is a block diagram of one embodiment of still another controlsystem that can be used with the drive system of FIG. 1.

FIG. 26 is a block diagram of one embodiment of a yet another controlsystem that can be used with the drive system of FIG. 1.

FIG. 27 is a flowchart describing one embodiment of a control processthat can be used with the drive system of FIG. 1.

FIG. 28 is a flowchart of a transmission and/or prime mover controlsubprocess that can be used with the process of FIG. 27.

FIG. 29 is a flowchart of a transmission control subprocess that can beused with the subprocess of FIG. 28.

FIG. 30 is a flowchart of a subprocess for determining a speed ratio ofa CVT, which subprocess can be used with the transmission controlsubprocess of FIG. 29.

FIG. 31 is a flowchart of a subprocess for controlling a shift actuatorof a CVT, which subprocess can be used with the transmission controlsubprocess of FIG. 29.

FIG. 32 is a chart representing a speed ratio of a CVT versus vehiclespeed lookup table that can be used with the subprocess, of FIG. 30, fordetermining a speed ratio of a CVT.

FIG. 33 is a data table used to derive the chart of FIG. 32.

FIG. 34 is a cross-sectional view of a CVT that can be used with thecontrol systems described here.

FIG. 35 is a cross-sectional view of a shifting mechanism for a CVT thatcan be used with the control systems and methods described here.

FIG. 36 is a cross-sectional view of a CVT variator mechanism foradjusting the speed ratio of a CVT, which can use the shifting mechanismof FIG. 36.

FIG. 37 is a schematic diagram that shows certain kinematicrelationships of a ball planetary CVT.

FIG. 38 is chart that presents data illustrating the power leveldelivered to the wheel of an EV when equipped with a CVT and whenequipped with a fixed ratio drive.

FIG. 39 is a chart that presents data illustrating the torque versusspeed relationships for an EV equipped with a CVT and for an EV equippedwith a fixed ratio drive.

FIG. 40 is a perspective view of an exemplary controller that can beused EV drivetrains disclosed here.

FIG. 41 is an exploded perspective view of certain components of thecontroller of FIG. 40.

FIG. 42 is a partial, cross-section showing certain components of thecontroller of FIG. 40.

FIG. 43 is an exploded, assembly view of an actuator control circuitboard and a drive motor control circuit board that can be configured foruse with the controller of FIG. 40.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

The preferred embodiments will now be described with reference to theaccompanying figures, wherein like numerals refer to like elementsthroughout. Inventive embodiments may include several novel features, nosingle one of which is solely responsible for its desirable attributesor which is essential to practicing the inventions herein described. TheCVT/IVT embodiments described here are generally related totransmissions and variators disclosed in U.S. Pat. Nos. 6,241,636;6,419,608; 6,689,012; 7,011,600; U.S. patent application Ser. Nos.11/243,484 and 11/543,311. The entire disclosure of each of said patentsand patent applications is hereby incorporated herein by reference.

A typical powertrain of an electric vehicle (EV) includes a power source(for example, a battery), an electric drive (for example, a drive motorand a drive motor controller), and a fixed-gear transmission device (forexample, sprockets, chain, gearing, etc.). Usually an EV uses adirect-drive configuration where the operating speed of the EV is linkeddirectly to the speed of the electric drive motor by a fixed gear ratio(or, in other words, a fixed transmission speed ratio). This is a simpleconfiguration, and no variable transmission speed ratios areimplemented, usually at the expense of efficiency and/or performance(for example, limiting acceleration and maximum speed of the EV).

However, an EV system can be improved by incorporating a continuouslyvariable transmission (CVT) into the EV drivetrain. When a CVT is usedin an EV, vehicle performance can be improved because the drivetrain canbe optimized at particular operational speeds and load conditions. A CVTalso improves the efficiency of an EV. The efficiency of the electricmotor is a function of operating speed and load, and battery life is afunction of current draw. A CVT and a suitable controller allow thedrivetrain to operate at speeds of the drive motor, and with selecteddrive motor current management, such that overall efficiency and rangecan be improved. In one embodiment, the CVT is a NuVinci® CVT, which isa compact, high torque-density unit that uses a planetary configurationbased on spheres and traction to provide continuously variable speedratio control.

By way of example, a NuVinci® CVT and a suitable control system (suchthose inventive embodiments described herein) can provide smooth,seamless shifts of the transmission speed ratio across the full range ofspeed ratios. In addition, since there are no fixed gear ratios, thecontrol system is able to control component speeds precisely, allowingthem to operate substantially at their optimal speed for a givenoperating condition. In some embodiments, the control logic also allowsprogramming for different conditions, allowing the user (ormanufacturer) to decide when performance or range is ultimately desired.Certain configurations of the NuVinci® CVT are easily packaged on an EV,and do not significantly affect the cost or the weight of the EV.

Additionally, users demand different operating characteristics from EVs.Some users are concerned with maximum range, while other users care moreabout performance factors (for example, vehicle launch, maximum speed,and hill climbing at speed). In the case of an inexperienced user,desiring maximum efficiency and range, the user might operate the EV ina fashion that provides better performance (for example, a quickerlaunch and/or higher maximum speed of the EV), but ultimately causes themaximum range to suffer dramatically because of high current draw andoperation of the electric drive motor at an inefficient speed. However,when combined with a suitable control system for optimal drivetrainoperation, a CVT can allow the EV to operate in a desired mode, such asa performance mode or an efficiency mode. In performance mode, range andefficiency are less important than outright performance, and thetransmission control system optimizes for acceleration, maximum speed ofthe EV, and hill climbing at speed, for example. In efficiency mode,range is the priority, so the control system keeps the drive motor atits most efficient speed and imposes limits on current draw from thebattery, for example.

In one embodiment, a control strategy uses data for motor efficiencyversus motor speed and motor torque, as well as battery life versuscurrent draw, to improve performance and efficiency of the overallsystem. Analysis models indicate that there are benefits of using a CVTin EVs, and the results of the modeling have been confirmed by empiricaltesting of CVT-equipped EVs that were compared to benchmark stockvehicles (fixed-gear ratio).

The typical duty cycle of an EV is highly dynamic because it involvesnumerous stops and starts, uneven terrain, and variable wind resistance.A drivetrain with a CVT can benefit an EV that operates over thesedynamic speed and load conditions by allowing the drive motor to operatecloser to its peak power or peak efficiency over a broad range of agiven duty cycle. Generally, when coupled to a CVT a propulsion sourceis capable of generating more torque and more speed than when coupledwith a fixed gear ratio transmission. As compared to a fixed-gear ratioconfiguration, a CVT lower gear ratio can allow for better launch feeland better hill climb ability, while a CVT higher gear ratio can allowfor higher maximum speeds. Additionally, in certain circumstances,increased acceleration of the EV is possible because the CVT changes theeffective inertia seen at the drive motor.

In one embodiment, the CVT is installed in a recreational-type LEV usingan in-wheel configuration where the housing of the CVT also forms thespokes and rim of the wheel. A drive motor is configured to transferpower to the transmission via a chain and sprocket coupled to thetransmission. Alternative methods of integrating the CVP to a vehicleinclude mounting the CVP to the chassis or the drive motor, orintegrating the wheel, CVP, and drive motor as one unit, for example.

Referencing FIG. 37, there is shown the system kinematics of awell-known CVT, where r_(i) is the contact radius of the input contact,and r_(o) is the contact radius at the output contact. The transmissionspeed ratio is determined by the tilt angle of the ball axis, whichchanges the ratio of r_(i) to r_(o), and thus the transmission speedratio. The result is the ability to sweep the transmission through theentire ratio range smoothly.

Two features allow the NuVinci® CVT to provide continuous gear ratiorange operation in a small package. The first is the geometricconfiguration of the drive, which is based on differential contact radiiof a sphere. Contacting a rotating sphere at two different locationsprovides a “gear ratio” (that is, a transmission speed ratio), which canrange from underdrive to overdrive depending on the location of thecontact points for input and output speed. The spheres are placed in acircular array around a central traction component and contact an inputring and an output ring. Continuously variable transmission speed ratiosare possible by tilting the rotational axis of the spheres (that is,varying the contact radii between the spheres and the input and outputrings). This configuration allows input and output to be concentric andcompact. The result is the ability to sweep the CVT through the entireratio range smoothly.

The second feature the NuVinci® CVT exhibits is a traction fluid. Atypical traction drive uses a traction fluid that under normalcircumstances and pressures provides lubrication for the drive. When thetraction fluid undergoes high contact pressures, the fluid undergoes aphase change and becomes a tractive solid. Within a traction patch,molecules of the fluid stack up and form a solid through which shear andtorque can be transferred. In one embodiment, the CVT for an EV usesmultiple spheres to transfer torque through multiple traction patches.

In one inventive embodiment, a drive motor and a transmission controllerare configured to optimize the drive-train components of the EV. Thehardware can be provided as an add-on controller that works inconjunction with the existing motor controller of the EV, or as astand-alone integrated controller. In the case of the add-onconfiguration, in one embodiment, correct CVT speed ratio can bedetermined from a speed sensor and a throttle position (interceptedbetween the throttle and the drive motor controller). For the integratedcontroller, control of the drive motor and of the CVT can be joined moreintimately, thereby increasing efficiency, simplicity, and reducingcost. The control system can react to driving conditions and isconfigured to keep the drive motor in an optimal range for a givenoperating condition. As used here, the term “operating condition” refersto a vehicle operating parameter, environmental state, and/or userselections, commands, or inputs. Additionally, the control system cantake into account battery state of charge and duty cycle efficiency tohelp manage power consumption.

In one case, the NuVinci® CVT is installed in an EV. In one example, theCVT is integrated into the rear wheel of the EV, and the CVT speed ratiois controlled automatically via a shift actuator and an electroniccontrol system.

In one embodiment, the EV application of the NuVinci® CVT uses a shiftactuator and a suitable control system to allow continuous and optimizedshifting. The EV is equipped with an electronic controller that monitorssystem operating parameters (for example, battery current, wheel speed,shift position, etc.) to control the CVT and the drive motor in closedloop control. Although the NuVinci® is used here as an example,inventive embodiments described here can be used with various types ofCVTs, including belt-pulley CVTs, toroidal CVTs, cone-based CVTs, MilnerCVT, hydrostatic CVTs, and the like.

In some embodiments, the control system can optimize the drive motorspeed, battery current, and transmission speed ratio based on, forexample, drive motor and CVT efficiency maps. In one example, the systemseeks to keep relatively constant the speed of the drive motor and/or tolimit the maximum current draw from the battery.

In one embodiment, a shift actuator is configured to shift the speedratio of the transmission. In certain embodiments, the transmissioncontrol system can be integrated with the motor controller (singlecontrol unit per vehicle), or can operate in conjunction with a drivemotor controller already provided with the EV. The transmissioncontroller can be configured to read drive motor current draw, drivemotor speed, wheel speed, and/or battery voltage to determine the bestCVT speed ratio for a given operating condition. This allows the drivecomponents to operate at optimal speeds for the given operatingconditions (including taking into account the selected mode ofoperation).

In one study, the Currie IZIP 1000 scooter (a direct-drive EV) was usedfor simulation and analysis. Vehicle dynamics equations illustrate thepossible performance advantages of a CVT added to this direct-drive EV.The equation of longitudinal motion is:

M _(v) a _(v) =F _(t) −F _(f) −F _(w)  (1)

where: M_(v)=mass of the vehicle and rider; a_(v)=acceleration of thevehicle and rider; F_(t)=tractive force at the drive wheel; F_(f)=forcedue to total road loads; F_(w)=force due to aerodynamic drag.

Equations for the forces above can be stated as:

$\begin{matrix}{F_{t} = \frac{\left( {T_{m} - {I_{{eq}_{m}}\alpha_{m}}} \right)i_{o}i_{cvp}\eta_{cvp}}{r_{d}}} & (2) \\{F_{f} = {M_{v}{g\left( {f_{r} + {slope}} \right)}}} & (3) \\{F_{w} = {\frac{1}{2}\rho \; C_{d}A_{f}v^{2}}} & (4)\end{matrix}$

where: T_(m)=torque output of the drive motor; I_(eq) _(m) =equivalentreflected inertia at the drive motor; α_(m)=angular acceleration of thedrive motor; i_(o)=gear ratio of the drive motor to the CVP (motorspeed/CVP input speed); i_(cvp)=gear ratio of CVP (CVP input speed/CVPoutput speed); η_(cvp)=efficiency of CVP; r_(d)=effective radius of thetire; g=acceleration due to gravity; f_(r)=rolling resistancecoefficient; slope=elevation divided by distance; ρ=density of air;C_(d)=aerodynamic drag coefficient; A_(f)=frontal area of vehicle andrider; v=velocity of vehicle and rider.

The equivalent reflected inertia at the drive motor shaft is given by:

$\begin{matrix}{I_{{eq}_{m}} = {I_{m} + \frac{I_{w}}{i_{o}^{2}i_{cvp}^{2}}}} & (5)\end{matrix}$

where: I_(m)=rotational inertia of the motor, and I_(w)=rotationalinertia of the wheel.

These equations provide a framework to determine acceleration, hillclimb ability, and maximum speed improvements possible for a Currie IZIP1000 scooter equipped with a CVT.

For vehicle launch, initial speed and aerodynamic drag are zero. At thisinstant, the acceleration of the vehicle is determined from Equations 1through 4 and is:

$\begin{matrix}{a_{v} = {\frac{\left( {T_{m} - {I_{{eq}_{m}}\alpha_{m}}} \right)i_{o}i_{cvp}\eta_{cvp}}{M_{v}r_{d}} - {gf}_{r}}} & (6)\end{matrix}$

Using values representative of the Currie IZIP 1000 scooter, thisanalysis indicates that initial launch acceleration (a_(v)) can beincreased up to 45% by implementing a CVT into the system. This resultassumes that the EV is not traction limited by the traction capacity ofthe tires, and that the acceleration is stable and controllable.

Further, FIG. 38 shows that for a representative drive motor curve, theCVT allows the drive motor to reach the peak power condition at a lowerspeed of the EV than with a fixed ratio configuration.

The CVT can also have a significant effect on reflected inertia at themotor shaft, as defined in equation 5. A higher gear ratio reduces therotational inertia reflected at the drive motor, and thus increasesacceleration for a given torque. With the ability to modulate theequivalent inertia at the drive motor shaft, the control system can usethe CVT to manage acceleration at all portions of the drive cycle.

A reasonable metric for hill climb capability can be defined as themaximum steady state speed that can be achieved on a given slope.Because this is a steady state metric, the acceleration component ofequation 1 is zero and we can determine the speed for a given slope bycombining equations 1 through 4 and solving for steady state velocity:

$\begin{matrix}{v = \sqrt{\frac{{2T_{m}i_{o}i_{cvp}\eta_{cvp}} - {M_{v}{g\left( {f_{r} + {slope}} \right)}r_{d}}}{\rho_{a}C_{d}A_{f}r_{d}}}} & (7)\end{matrix}$

Another metric of interest is the maximum slope the vehicle and ridercan climb at a given velocity, which is simply solving equation 7 forsteady state slope:

$\begin{matrix}{{slope} = {\frac{{T_{m}i_{o}i_{cvp}\eta_{cvp}} - {\frac{1}{2}\rho \; C_{d}A_{f}v^{2}r_{d}}}{M_{v}g\; r_{d}} - f_{r}}} & (8)\end{matrix}$

Using values representative of the Currie IZIP 1000 scooter, it can beshown that a CVT equipped scooter can theoretically obtain at least a69% increase in steady state velocity up a given slope. It should benoted that this is the case because in the stock scooter the speed ofthe drive motor drops below its base speed, where the drive motordelivers less power. It can also be shown that the maximum slope the EVand rider can climb increases by at least 45% with a CVT.

Additionally, steady state torque at the rear wheel (T_(w)) can bedefined from Equation 2 as:

T _(w) =F _(t) r _(d) =T _(m) i _(o) i _(cvt)η_(cvt)  (9)

Applying a generic torque curve for a typical, controlled, brushed DCmotor (as shown in FIG. 39), commonly used in some EVs, and applying theCVT ratio in equation 9, we can determine the effect that the CVT has inincreasing the overall operating range of the EV. FIG. 39 shows that inunderdrive the CVT increases the torque delivered to ground andincreases the hill climb capability of the EV.

Maximum speed is defined as the maximum speed a vehicle and rider canreach at steady state, with no grade. Similar to the hill climb,acceleration is zero at this condition and there is no dependence onsystem inertia.

Two scenarios can define the maximum possible speed for an electricvehicle. If the drive motor can spin freely to its maximum speed, thevehicle is said to be motor speed-limited. If the drive motor cannotovercome the total road load and aerodynamic forces before reaching itstop speed, the vehicle is said to be power-limited.

If the vehicle is motor speed-limited, the maximum speed of the EV canbe increased by adding a CVT, as shown in the overdrive region of FIG.39. The vehicle can be geared such that, at the maximum speed of the EV,the tractive force at the wheel is completely opposed by the road loadsand aerodynamic drag. This is also governed by equation 7.

The Currie IZIP 1000 scooter is motor speed-limited, and therefore itbenefits from the addition of the CVT. Using equation 7 withrepresentative values for the Currie scooter, it can be shown that themaximum speed of the EV can be increased by up to 75%.

If the maximum speed of an EV is power-limited in a fixed ratioconfiguration, the addition of a CVT might not increase the maximumspeed of the EV. The reason being that beyond its base speed theelectric drive motor provides constant power (as shown in FIG. 37). Atransmission does not add power to the system. Hence, if the total roadload and aerodynamic drag has matched the power limit of the EV, the EVis not likely to accelerate further. It should be noted, however, thatfor the operating range of certain EVs on the market today (for example,scooters, neighborhood electric vehicles, etc.), the maximum speed ofsuch EVs is not power-limited.

It is apparent that a CVT in an EV increases performance in differentcategories, including launch acceleration, hill climb ability, andmaximum speed of the EV. To improve operating range on a single batterycharge, however, the control system preferably takes into accountbattery performance, as well as drive motor and transmission efficiency.Additionally, the control system is preferably configured to take asystems approach to controlling all the components to conditions thatoptimize overall system efficiency.

The operating range of an EV is dependent on the drive cycle (forexample, frequency of stops and starts and hill climb and descent). Fora preliminary analysis, a drive cycle was used that included no stops,four substantial elevation changes, and speeds ranging from 16-kph to24-kph on the stock Currie IZIP 1000 scooter.

A dynamic simulation was created to model the performance of a 1000 Wscooter over the chosen drive cycle. The simulation included thefollowing features: (a) dynamic permanent magnet DC motor model(including measured efficiency data), (b) dynamic CVP model (includingmeasured efficiency data), (c) total road load and aerodynamic dragmodel, (d) battery model where voltage drops as a function of currentdraw, and (e) current limiter that limits input power to the drivemotor.

A control process simulated control of the transmission speed ratio ofthe CVT to shift the CVT when an efficiency improvement could beachieved. Otherwise, the control process kept the CVT at thetransmission speed ratio of peak efficiency. The simulation showed thatfor the given duty cycle, the CVT-equipped scooter approximately matchedthe range performance of the stock scooter while still providingimprovements in hill climb, acceleration, and maximum speed of the EV.

To empirically evaluate the impact of the use of a CVT in an EV, testswere conducted to benchmark the performance of a stock (that is,unmodified) EV against a vehicle equipped with a CVT and a suitablecontrol system. The test EV was the 2006 model Currie IZIP 1000 scooter.

A NuVinci® CVT was integrated into a rear wheel design, which iscompatible with the frame of the stock scooter. Tests were conductedwith a data acquisition system fixed to the vehicle that included a datalogger, supply battery, and various sensors and wiring. Four tests wereperformed, including standing start acceleration, maximum speed, hillclimb ability and range. For acceleration, hill climb, and range tests,the system control software limited the maximum speed of theCVT-equipped scooter to match approximately the maximum speed of thestock scooter. The acceleration test was conducted from a standing starton flat asphalt and used a predetermined start line and an infraredphotogate for the finish line at a distance of 0.2-km. Speed data wasused to obtain acceleration times from 0-kph to 16-kph and 0-kph to19-kph, and the time to complete the distance. The maximum speed of thescooter was measured as an independent test on flat asphalt with thespeed limit removed. The system was manually set to its maximum,possible sustained vehicle speed, and speed data was recorded. The hillclimb benchmark was performed on a predetermined hill with a subtlyincreasing grade over a fixed distance of 0.75-km. The range testinvolved driving the vehicle continually over a 5.15-km loop until themaximum, sustained vehicle speed dropped below a predetermined level.The course included a variety of grades and two stops and starts. Inaddition to collecting data on vehicle performance, drive cyclecharacteristics (such as GPS data, elevation, and hill grade) wererecorded to characterize a typical drive cycle of an EV used forcommuting.

The results of the benchmark tests indicate significant increases inperformance and hill climb capability. The 0-kph to 16-kph and 0-kph to19-kph times represent 25% and 24% increases, respectively, with the useof the CVT and the control system. Additionally, the time to completethe hill climb test was almost halved, and there was an 85% increase inaverage speed.

With the speed limit removed in the control system software, theCVT-equipped vehicle achieved a maximum speed of 34-kph, whichrepresents a 61% increase over the maximum speed of the stock vehicle.This indicates that the maximum speed of the stock vehicle is notpower-limited, but rather, is motor speed-limited.

Some of the factors influencing the range results with the CVT-equippedEV include that the maximum speed limit of the CVT-equipped EV was setslightly higher than with the stock EV, yielding higher aerodynamiclosses. Additionally, the drive motor controller allowed the battery todeliver slightly higher current with the CVT-equipped EV. It is notablethat the CVT and the control system provided substantial performanceimprovements with negligible impact on range. The benefits realized are,in part, a result of controlling the drive motor and the transmission asa system.

The stock scooter showed reasonable consistency in performance data, butfailed to climb hills with a 10% without overloading the drive motorcontroller. With an adult rider, the advertised maximum speed of thestock scooter could not be achieved.

In some embodiments, the controller can be configured to facilitatedifferent modes of operation. In some cases, it is preferable to have aneconomy mode where the EV is used for commuting or a performance modewhere the EV is used for recreation. Although not as efficient, manualshifting of the transmission can provide a unique and fun aspect torider experience. The desired controller mode can be selected through anexternal user interface, throttle position, or can be set by the controlsystem automatically by analyzing driving parameters, inputs, andhistory.

EVs that employ regenerative braking can also benefit from use of theCVT and control system. The control system can be configured to commandthe CVT to allow the drive motor to operate at its most efficient speedfor generating energy to supply back to the battery system, whenregeneration is required during braking or extended descents.

Described in the following are various inventive embodiments ofdrivetrains for EVs that incorporate one or more configurations of CVTs,drive motor, and suitable controllers and processes for optimizing EVperformance, range, etc., under various operating conditions and/ordesired operating modes. As used here, the terms “drivetrain” and“powertrain” are used interchangeably; it should be understood that insome embodiments a drivetrain includes references to a power source,such as a battery.

Referencing FIG. 1 now, a drive system 10 includes a prime mover 12coupled to a continuously variable transmission (CVT) 14, which iscoupled to a load 16. In one embodiment, a control system 18 is adaptedto receive information from the prime mover 12, CVT 14, and/or load 16.The control system 18 can also be adapted to provide commands to oractuate the prime mover 12 and/or the CVT 14. The prime mover 12 can beany source of power, such as an electric motor, internal combustionengine, wind turbine, a combination thereof, etc. The electric motor canbe, for example, a brushed DC motor, a brushless DC motor, a permanentmagnet motor, or any other type of electric motor. The load 16 can be atractive load, which can include the weight of vehicle and/or anoperator and/or cargo and passengers. The CVT can be a ball planetaryCVT, a toroidal CVT, or a belt-and-pulley CVT, for example. In oneembodiment, a drive system 10 includes a NuVinci® continuously variableplanetary, and a drive mechanism between the prime mover and the CVT.The drive mechanism can be, for example, a chain and sprocket drive, adirect gear drive, or any other type of power transmission gearing. Insome embodiments, the control system 18 includes sensors, actuators, andcontrol hardware, firmware, and logic as described further below.

The system, or subassemblies thereof, shown in FIG. 1 can be adapted foruse in any ground, air, or water transportation machine, industrial oragricultural equipment, aerospace vehicles and equipment, and householdmachines, to name a few applications.

FIG. 2 illustrates one embodiment of a control system 18 that includes acontroller 20 in communication with sensors 22, a data display and userinterface 24, a mechanical actuator 26, and the prime mover 12. In oneembodiment, the controller 20 includes electronic hardware 28 incommunication with control logic 30. In some embodiments, the sensors 22are adapted to sense conditions of the prime mover 12, load 16, and abattery 32, which can be configured to provide power to the prime mover12. The battery 32 can be, for example, a 36V battery.

Referencing FIG. 3 now, in one embodiment, a controller 302 can controlthe CVT 14 and the prime mover 12 to maximize the performance andefficiency of a vehicle. This embodiment can be referred to as anintegrated control in that most or all of the control components andfunctionality used to control the CVT 14 and the prime mover 12 can beintegrated in a single controller 302, which in some embodimentsincludes a single electronic board. In one embodiment, the controller302 can be adapted to receive a throttle input (which can be a voltagesource).

In one embodiment, a control system 300 can include an actuator motor304 to actuate a shift (that is, an adjustment) of the speed ratio ofthe CVT 14. The CVT 14 can be coupled to the drive wheel assembly of avehicle, for example. In one embodiment, the system includes sensors.These can include a wheel speed sensor 306 for sensing wheel speedand/or a motor speed sensor 308 for sensing the speed of the drivemotor. The sensors 306, 308 can be any type of speed sensor, for examplean active magnetic sensor, passive magnetic sensor, or encoder of anytype. In some embodiments, the speed of the drive motor 12 can be senseddirectly in a controller 340 by measuring the frequency of electriccurrent supplied to the drive motor. Similarly, there can be an actuatorposition sensor 310 that can be, for example, an encoder orpotentiometer. In some embodiments, the actuator position can be derivedfrom the measured speed ratio of the CVT 14. The speed ratio of the CVT14 can be calculated from the wheel speed, speed of the drive motor 12,and any gear ratios in the system. The system 300 can additionallyinclude a throttle position sensor 312, a battery fuse switch and/orsensor 314, and a brake cut-off switch and/or sensor 316, any of whichcan be configured to provide signals to the controller 302.

FIGS. 4 and 5 show different views of one embodiment of a drive system400. A frame 402 of a vehicle (a scooter, electric bicycle, ormotorcycle, for example) supports a drive motor 404 that is coupled to aCVT 406 via a pinion 408, a chain 410, and a sprocket 412. In thisembodiment, the CVT 406 is integrated in the rear wheel hub of thevehicle and it drives a rim 414 via spoke 416. A shift actuator 418 iscoupled to the CVT 406. The shift actuator 418 can include a shiftactuator motor and suitable gearing (such as reduction gears, forexample).

In one embodiment, the control system 18 includes a user interfacedevice 502 as shown in FIG. 6. The interface device 502 can display atleast some of the operating parameters of the system 10, for example,battery voltage, speed of the drive motor 12, speed of the vehicle 506,throttle position, speed ratio of the CVT 14, or mileage. Mileage can bedisplayed in terms of Watt-hrs/mile or some other units. The interfacedevice 502 can be equipped with input buttons 504 to allow selection ofdifferent modes of operation while stopped or driving. The interfacedevice 502 can be integral with the vehicle 506. Alternatively, theinterface device 502 can be removable, with attachment hardware thatallows easy removal of the interface device 502. The interface device502 can be configured to record data of any signal generated or derivedfrom the controller 340. Data can be recorded at periodic frequency, forexample, a reading of all measured or derived signals every 50 ms.

A machine equipped with the control system 300 offers advantages overcontrol systems with either a fixed ratio chain drive or a manuallycontrolled CVT. In one embodiment, the controller 302 manages the speedand current of a drive motor 12, the current draw from a battery, andthe speed ratio of the CVT 14 to optimize the efficiency, acceleration,hill climb capability, and ride feel of a given vehicle, whileminimizing noise. The controller 302 can be assembled and operated inseveral configurations. For example, the controller 302 can include adrive motor controller 302A, for controlling the drive motor 12, as wellas a CVT controller 302B, for controlling the CVT 14, all integrated onone board, as shown in FIG. 7.

Alternatively, the controller 302 can be operated to control only theCVT 14 and to cooperate with an existing drive motor controller 320installed on a given vehicle. In this configuration, the drive motorcontroller 302A in the fully integrated configuration of Figure G isdisabled and the CVT controller 302B cooperates with the separate motorcontroller 320, as shown in FIG. 8. In this configuration, the CVTcontroller 302B can sense and communicate different operating parametersgenerated by the separate motor controller 320.

In either configuration, the controller 302 can control the drivetrainbased on several inputs, such as speed of the drive motor 12, vehiclespeed, current of the drive motor 12, or throttle signal.

In some embodiments, the control system 18 can have several modes ofoperation. In an acceleration mode (“drag race”), vehicle accelerationis maximized by quickly setting the CVT 14 in a full underdriveconfiguration as the vehicle launches, thus allowing the drive motor 12to accelerate to its highest power condition and providing mechanicaltorque advantage to the drive motor 12. As the vehicle accelerates, thecontrol system 18 shifts the CVT 14 according to the speed of thevehicle such that the speed of the drive motor 12 is held at the peakpower condition of the drive motor 12 according to the torque, currentdraw, and speed of the drive motor 12. In one embodiment, inacceleration mode the control system 18 can control the electricalcurrent between the battery 32 and the drive motor 12 in several ways.For example, the control system 18 can limit the maximum allowablecurrent or the length of time above a certain current level, for example65 Amps (A).

In a range mode (“economy”), the operating range of the vehicle on asingle battery charge is maximized by controlling the acceleration andtop speed of the vehicle to minimize power usage during driving. Thecontroller 20 controls the speed ratio of the CVT 14 to allow the drivemotor 12 to operate at its most efficient speed through all operatingconditions in a given driving cycle. Further, the controller 20 canminimize the maximum current draw from the battery and the length oftime operating above a certain current condition.

In a fixed ratio simulation mode (“stepped”), the control system 18 cancontrol the CVT 14 to simulate the operation of a multispeedtransmission. For example, during a wide open throttle acceleration, thecontroller 20 controls the speed ratio of the CVT 14 to a constantunderdrive value, for example 2:1, and allows the speed of the drivemotor 12 to accelerate through the operating range of the drive motor12, for example from 500 rpm to 3500 rpm, as the vehicle accelerates.The controller 20 then quickly shifts the CVT 14, for example in lessthan 500 ms, to a higher speed ratio, for example 1.5:1 whilesimultaneously allowing the speed of the drive motor 12 to quickly dropback to a low speed, for example 500 rpm. Then the controller 20 repeatsthe same acceleration of the drive motor 12 and continues vehicleacceleration while holding constant the speed ratio of the CVT 14. Thecontroller 20 can repeat this procedure for any number of speed ratiosof the CVT 14, for example 5 or 6 settings. The mode of operationdescribed by the fixed ratio simulation mode is similar to the “sawtooth” acceleration shown in FIG. 9.

In a hill climb mode, the performance of the vehicle while climbing ahill is maximized. In hill climb mode, the control system 18 controlsthe CVT 14 to a low speed ratio such that the drive motor 12 has amechanical advantage as compared with a fixed ratio vehicle driveline.Additionally, the controller 20 can optimize the current draw to thedrive motor 12 to manage the power delivered to the ground to optimizethe ability of the vehicle to climb the hill.

In a manual mode, the control system 18 allows an operator to controlmanually the CVT 14. In manual mode, the user can use buttons, forexample, on the user interface device 502 to increase or decrease thespeed ratio of the CVT 14. In some embodiments, the operator canadditionally select the mode (for example, economy, hill climb, etc.)using the user interface device 502.

In any of the modes described above, the top speed of the vehicle andthe drive motor 12 can be controlled to any desired value within thefull operating ratio range of the CVT 14 and the drive motor 12.

The operating modes described above can provide performance improvementsof a vehicle equipped with the control system 18 and a CVT 14 versus aconventional fixed ratio drive system. FIG. 10 presents an example ofobserved performance differences and/or improvements.

FIG. 11 shows a schematic diagram of one embodiment of a control system600. The control system 600 can include several subsystems, such as apower control module 610, a USB Interface 620, a test interface 630, acontroller 640, a main Drive 650, a user interface 660, an actuatorcontrol module 670, SPI 680, a com interface 690, and a power monitor695.

FIG. 12 shows one embodiment of the power control module 610. The powercontrol module 610 receives power from the battery 32 and incorporatesvoltage regulators and signal conditioners to regulate the outputvoltage into several distinct steady levels, possibly including forexample 3 volt (V), 5V, 15V, 36V. The power control module 610 canprovide an analog diagnostic signal of the battery voltage to thecontroller 640. In one embodiment, the power control module 610 includestwo connections points TERM5 101 and TERM6 102, which represent thepositive and negative lines coming from the 36V battery. In someembodiments, the power control module 10 has six built-in connectionpoints that enable the power control module 610 to communicate withother subsystems on the control system 600. A connection VCCP3_3Vsupplies a steady 3.3V supply rail to the rest of the system. Aconnection VCCP5V supplies a 5V, VCCP15V supplies 15V, and VCCP36VO isthe battery voltage supply rail to the entire system. BAT_VFB is ananalog voltage signal that is sent to the controller 640 to monitor thevoltage of the battery 32 during operation.

FIG. 13 shows a USB interface 620, which includes a Universal Serial Bus(USB) interface that allows a user to connect external programming ordata acquisition hardware, for example a personal computer, to thecontrol system 600 and specifically interface with hardware on thecontroller 640. In one embodiment, the USB interface 620 includes sixconnection points. The USB interface 620 is powered by VCCP5V andVCCP3_3V. The remaining four connections are common to a typical USBinterface. The lines marked DDn and DDp are differential data pairs thatenable the controller 640 to recognize the device connected to the USBport. The line marked VB is the 5V bus detector. The PC line is the pullup control.

FIG. 14 shows one embodiment of the test interface 630. Among otherthings, the test interface 630 allows developers to access the hardwareon the control system 600 and, in particular, to access components builtinto the controller 640. The test interface 630 has specific test pointsbuilt into the board to measure voltage and confirm operation of variouscomponents. In one embodiment, the test interface 630 functions as theport through which firmware is downloaded to the controller 640. Thetest interface 630 can contain a series of headers or connector pins sothat a developer can connect external programming hardware, for examplea computer.

In some embodiments, there are twelve connection points in the testinterface 630. The test interface receives signals from the VCCP5V andthe VCCP3_3V to power the subsystem for its communication with thecontroller 40. The test interface 30 can be adapted to communicate withthe controller 640 through connections that are organized into industrystandard functional groups. The lines labeled SEL, TDI, TMS, TCK, TDO,and NRST are part of an IEEE standard 1149.1 for Standard Test AccessPort and Boundary-Scan Architecture for test access ports used fortesting printed circuit boards. This standard is often referred to asJTAG, an acronym for Joint Test Action Group. The lines labeled TST andERASE are used to put the controller 640 into different modes and erasethe flash memory, respectively. The lines labeled DTXD and DRXD are partof a known connection type called a universal asynchronousreceiver/transmitter (UART), which is computer hardware that translatesdata between parallel and serial interfaces. These connections are usedfor serial data telecommunications, a UART converts bytes of data to andfrom asynchronous start-stop bit streams represented as binaryelectrical impulses.

FIG. 15 shows one embodiment of the controller 640, which contains amicrocontroller, firmware, random access memory, flash memory, and otherhardware peripherals to allow communication between the controller 640and other subsystems of the control system 600. The controller 640 holdsa majority of the control processes for the controller 640, which isused to manage operations of the control system 600. Certain subsystemshave several connections to communicate with the controller 640. Theseconnections are described in correlation with the subsystems disclosed.In addition to those connections, there can be additional connectionpoints or headers included in the board of the controller 640 formiscellaneous use. For example, referencing FIG. 11, there are threepins TP4, TP1, and TP2.

FIG. 16 illustrates one embodiment of the main drive 650. The main drive650 can be adapted to control the drive motor 12. There are severalpower connections to the main drive 650, which utilizes power from theVCCP36V line that is connected directly to TERM4 on the drive motor 12.The DRV_PWM line represents a pulse width modulated current signal thatthe controller 640 generates to control the current that passes to thedrive motor 12 and thus control the torque the drive motor 12 applies tothe system 10. The BRAKE line delivers a signal from the brake detectionswitch that can be installed on the vehicle under the brake lever, forexample, to detect when the operator engages the brake. If the brake isengaged, the BRAKE signal commands the main drive 650 to turn off toprevent damage to any component in the drivetrain or the control system600.

VCCP5V, VCCP3_3V, VCCP 15V are lines for 5V, 3.3V and 15V supplyvoltages respectively. The DRV_IFB line is the motor current detectionsignal from the main drive 650. DRV_IFB is an analog signal read by thecontroller 640. The firmware loaded on the controller 640 uses theDRV_IFB signal as feed back to control the drive motor and protectagainst over-current conditions that may arise during normal operation.The lines DRV_POS_A and DRV_POS_B can be used to detect the direction ofthe drive motor 12. In some embodiments, DRV_POS_A can be used tomeasure speed of the drive motor and DRV_POS_B can be used to detectoperating modes from the controller 640.

FIG. 17 shows one embodiment of a user interface module 660. The userinterface module 660 represents the communication with hardware theoperator uses to control the system 600. In some embodiments, the userinterface 660 includes the Brake, Throttle and Battery Voltage feedback.The user interface 660 can receive signals from VCCP36V and VCCP5V.

FIG. 18 illustrates one embodiment of a shift actuator control 670. Theshift actuator control 670 can be adapted to control the actuator motor304 (for example, see FIG. 3) that adjusts the speed ratio of the CVT14. The shift actuator control 670 is the physical interface to theactuator motor 304 and receives power from all of the regulated voltagelines. The shift actuator control 670 receives signals via ACT_DIR1 andACT_DIR0 from the controller 640 that define the direction of rotationof the actuator motor 304. The shift actuator control 670 can receive aPWM signal from the controller 640 via ACT_PWM that defines theelectrical power and current level going to the actuator motor 304.Similarly, ACT_IFB is a measurement signal indicating to the controller640 the current amperage to the actuator motor 304. The controller 640can include logic to limit and manage the current driving the actuatormotor 304. The shift actuator control 670 can receive signals from anactuator position sensor 310, for example, and quadrature encoder orpotentiometer and sends the signals to the controller 640 via ACT_POS_Aand ACT_POS_B.

FIG. 19 shows the serial peripheral interface (SPI) 680. In oneembodiment, the SPI 680 can be a standard synchronous serial data linkthat operates in full duplex mode. Devices communicate in master/slavemode where the master device initiates the data frame. Multiple slavedevices are allowed with individual slave select (chip select) lines.

FIG. 20 illustrates one embodiment of the com interface 690, which isthe physical interface for an interface module 502. The connectors shownin FIG. 11 are known transmitter/receiver pairs for communication withthe interface module 502.

FIG. 21 shows one embodiment of the power monitor 695, which monitorsthe operation of the system 600 and in the event of a loss of control orunexpected occurrence shuts down the system 600 by short circuiting thebattery lines and blowing the fuse of the system 600. The shutdowncommand is sent via D_RWAY and RUN_AWAY. The power monitor 695 caninclude a second microcontroller that makes decisions based on thesystem operation. The power monitor 695 monitors actuator current,A_IFB, and will disable power to the actuator motor via A_SHDN ifnecessary. In one embodiment, the power monitor 695 monitors the PWMsignal to the drive motor via D_PWM. The power monitor 695 can receive asignal VCCP3_3V.

Referencing FIG. 22, a control system 2200 can include a controller 2202adapted to receive inputs such as battery status, throttle position,throttle rate, vehicle speed, current in a drive motor 2204, speed ofthe drive motor 2204, a mode selection, and a position of an actuator2206 that adjusts a speed ratio of a CVT 2208. Based on at least some ofthese inputs, the controller 2202 commands a motion of the actuator2206. The controller 2202 can be additionally adapted to provide statusor other indicators to, for example, a user interface and/or to a datastorage device.

Passing to FIG. 23 now, a control system 2300 can include a controller2302 coupled to a drive motor 2304 and to an actuator motor 2306. In oneembodiment, the drive motor 2304 couples to a CVT 2308, which couples tothe actuator motor 2306. The controller 2302 can be adapted to receivesignals from an actuator position sensor 2310 and/or a wheel speedsensor 2312. In some embodiments, the controller 2302 can be adapted toreceive signals from a throttle position sensor 2314, a battery fuseswitch 2316, and/or a brake cut-off switch 2318. Signals from thebattery can include voltage and/or current signals indicating the statusof the battery.

Moving to FIG. 24 now, a control system 2400 can include a transmissioncontroller 2402 coupled to a shift actuator motor 2404. The shiftactuator motor couples to a CVT 2408. The transmission controller 2402can provide commands and/or power to the shift actuator motor 2404. Ashift actuator position sensor 2406 can be coupled to the shift actuatormotor 2404 or to a component of the CVT 2408. In some embodiments, awheel speed sensor 2410, which can be coupled to the CVT 2408, providessignals to the controller 2402. In one embodiment, the transmissioncontroller 2402 receives signals from a throttle position sensor 2412and/or a battery status sensor 2414, which couples to a battery orbattery fuse switch 2416.

In some embodiments, the transmission controller 2402 cooperates with adrive motor controller 2418 that is coupled to a drive motor 2420. TheCVT 2408 can be coupled to the drive motor 2420. In one embodiment, amotor speed sensor 2422, which can be coupled to the drive motor 2420,sends signals to the transmission controller 2402. A brake cut-offswitch 2424 can be adapted to provide signals to the drive motor 2418.In one embodiment, the transmission controller 2402 provides a throttlesignal to the drive motor controller 2418.

Thus, the control system 2400 can be configured such that a transmissioncontroller 2402 is used for controlling the speed ratio of a CVT 2408, adrive motor controller 2418 is used for controlling a drive motor 2420,and the controllers 2402, 2418 are configured to cooperate incontrolling a drive system, such as drive system 10 of FIG. 1.

Turning to FIG. 25 now, a control process and drive system 2500 caninclude sensors 2502 that provide signals to a controller 2504, which isadapted to control a shift actuator of a transmission and a drive motor.In one embodiment, energy is supplied to the system 2500 from battery2506, and the energy is ultimately converted to a mechanical actuationof a shifter mechanism of the transmission, and powering a wheel of avehicle via the drive motor, to provide an appropriate or desiredvehicle speed.

In one embodiment, a throttle input is provided to a throttle positionsensor 2508, a drive motor speed sensor 2510, and a motor power sensor2512. Vehicle inputs can be received from the motor power sensor 2512,vehicle speed sensor 2514, and a speed ratio sensor 2516 of thetransmission. Signals from the battery can be provided to the vehiclespeed sensor 2514 and to the drive motor speed sensor 2510.

The controller 2504 can be configured to determine at a module 2518 anoptimum drive motor speed (in rpm, for example) and/or at a module 2520an optimum motor power based on one or more signals provided by thethrottle position sensor 2508, drive motor speed sensor 2510, and/or themotor power sensor 2512. The controller 2504 can be configured todetermine at a module 2522 an optimum transmission speed ratio based onat least some of the signals provided by the throttle position sensor2508, the speed ratio sensor 2516, the vehicle speed sensor 2514, and/orthe motor power sensor 2512. The module 2522 can also use results fromthe modules 2518 and 2520 to determine the optimum speed ratio for thetransmission. In one embodiment, the controller 2504 includes a module2524 for determining battery use based on signals received from themotor power sensor 2512 and/or a battery power sensor 2526.

In some embodiments, the controller 2504 includes a drive command module2528 that receives signals from the optimum motor speed module 2518 andthe battery use module 2524. The drive command module 2528 governs thetransfer of power from the drive motor 12 to the wheel, for example, ofa vehicle. The drive command module 2528 can also be configured toprovide a feedback signal to the motor speed sensor 2510. The controller2504 can also include a command shift actuator module 2530 adapted togovern the actuation of a shifting mechanism of a transmission based, atleast in part, on results produced by the optimum speed ratio module2522.

Referencing FIG. 25A, a drive and control system 2550 includes a CVTactuator and controller 2552, which is adapted to receive power from asource such as a battery 2554. The actuator and controller 2552 canestablish an appropriate vehicle speed 2558 based on throttle input 2556and vehicle inputs 2560.

Passing to FIG. 26 now, a drive and transmission control system 2600 caninclude a microprocessor 2602, such as an Atmel ARM7 chip, that isadapted to cooperate with a number of software modules or processes. Anapplication programmer interface 2603 is in communication with a pulsewidth modulation module 2604, which cooperates with a motor controlmodule 2606. A drive motor control module 2608 is in communication withthe motor control module 2606 and a drive system control module 2610.The motor control module 2606 communicates with a position controlmodule 2612 that is in communication with a transmission control module2614. A main control module 2616 is in communication with the drivesystem control module 2610, a display output module 2618, a throttleposition module 2620, a battery fuel gauge module 2622, and/or a wheelspeed module 2624.

Turning to FIG. 27 now, a process 2700 of controlling a prime moverand/or a transmission is illustrated. The process 2700 starts at a state2702. The process 2700 moves to a state 2704, wherein an initializationroutine runs a number of processes. One process includes loading systemparameters and defaults such as maximum vehicle speed, transmissionshift limits, wheel pulse count, wheel size, etc.

The process 2700 then performs various subprocesses. The subprocessesincludes an analog-to-digital converter subprocess 2706, a memoryread/write subprocess 2708, a display IO subprocess 2710, a testsubprocess 2712, a motor control and throttle subprocess 2714, and aroad speed calculation subprocess 2716.

Referencing FIG. 28, the motor control and throttle subprocess 2714 canbe configured as a loop that repeats every 5-milliseconds (200 Hzrefresh), for example. In one embodiment, the motor control and throttlesubprocess 1014 includes a drive control module 2802 and a transmissioncontrol module 2804. The drive control module 2802, in some embodiments,can be any suitable pulse width modulation motor control scheme. In oneembodiment, the transmission control module 2804 includes a positioncontrol servo feedback loop. Hence, the motor control and throttlesubprocess can provide drive motor control and actuator motor positioncontrol.

In some embodiments, the motor control and throttle subprocess 2714starts at a state 2800. The process 2714 then substantiallysimultaneously executes the drive motor control module 2808 and thetransmission control module 2804. At a decision state 2806, thesubprocess 2714 determines whether the subprocess 2714 should continueto be executed in its loop. If the decision is to continue, thesubprocess 2714 resumes execution of the modules 2802, 2804. If thedecision is not to continue, the subprocess ends at a state 2808. Insome instance, at the decision state 2806 it is determined not tocontinue the subprocess 2714 because, for example, an off signal or abrake signal has been issued by the system.

In one embodiment, the drive control module 2802 handles the vehiclespeed demand and modulates the output of a drive motor. The drivecontrol module 2802 can also incorporate a soft-start routine tominimize abrupt shocks on a vehicle during high speed demand (that is,fast throttle ON). In one embodiment, the drive control module 2802accomplishes a soft start by regulating the maximum current that thedrive motor can pull and by delaying the throttle signal value,eliminating an instant-on effect.

Referring to FIGS. 29-31, in some embodiments, the initialization of thetransmission control module 2804 includes an actuator homing routine toposition the transmission at a desired state (for example, the tiltangle of the traction rollers, or power adjusters, is put in anunderdrive configuration) to begin a drive cycle. In one embodiment, thetransmission control module 2804 on startup drives the shift actuatormotor towards underdrive, while reading the position of a shift rod viacounts from an encoder on a shaft of the actuator motor. When thereading stops changing (for example, when the actuator motor has rotatedthe shift rod until the internal shifter assembly runs up against ashift stop), an actuator control process 3104 stops driving the actuatormotor and reads the initial shift position parameter from a shiftersubprocess 2902. In one example, the actuator control process 3104initially sets the transmission speed ratio to just above fullunderdrive (for example, 17 degrees gamma into underdrive; wherein, thefull underdrive range goes to 18 degrees gamma into underdrive). In oneembodiment, the actuator control process 3104 uses encoder counts as anindication of position. After actuator homing, the actuator controlprocess 3104 continues with further operations.

The transmission control process 2804, which begins at a starting state2900, determines a required transmission speed ratio (that is, the tiltangle of the traction planets) from a shifter process 2902 that handlesthe current state of inputs and from a lookup table with prescribedoutput values of speed ratio of the transmission. The transmissioncontrol process 2804 then passes the output set point to the actuatorprocess 2904, which applies power, via an actuator motor drive module2906, to the actuator motor until the set point is reached.

In one embodiment, the transmission control process 2804 receives a setof inputs to describe a state of the vehicle. In one embodiment, theseinputs include vehicle speed, drive motor current, and other parametersthat describe the state of the vehicle. In some embodiments, the mode ofthe controller is also determined. The mode can be selected manually viaa toggle switch or a button. In some embodiments, the mode can be aperformance (sport) mode or an economy mode. Yet in other embodiments,the mode can be a simulated 4-speed transmission “sawtooth” mode. Thecontroller can store mode tables in a memory. A mode table is a set ofdata that includes input parameters (for example, vehicle speed, motorcurrent, etc.) as well as a desirable speed ratio of the transmission asthe output parameter. Input values can be used to reference a table andproduce an output value. The output value is then passed over to theactuator process 2904.

The actuator process 2904 can be a proportional control feedback loopusing the set point for the speed ratio of the transmission as an input,with the actuator shaft encoder as a feedback signal. The actuator motordrive module 2906 can include a bi-directional (reversing) routine 2908,a motor drive routine 2910, and a suitable pulse width modulation (PWM)routine 2912. The transmission control process 2804 then ends at a state2914.

FIG. 30 depicts one embodiment of a shifter process 2902. The shifterprocess 2902 starts at state 3000. Vehicle speed 3002, drive motorcurrent 3004, and/or other parameters 3006 are received in a monitorvehicle status module 3008. The shifter process 2902 then moves to amode select state 3010, wherein a shift mode input 3012 can be received.The shifter process 2902, then proceeds to a decision state 3014,wherein the shifter process 2902 determines which shift mode to use. Ifthe shift mode selected is the sport mode, at a state 3016 the shifterprocess 2902 takes as input the sport mode lookup tables 3018. If theshift mode selected is the economy mode, at a state 3020 the shifterprocess 2902 takes as input the economy mode lookup tables 3022. If theshift mode selected is another mode, at a state 3024 the shifter process2902 takes as input the appropriate lookup tables 3026 for the selectedmode.

Based on the vehicle status and the mode selected, the shifter process2902 determines an optimal speed ratio for the CVT at a state 3028. Inone embodiment, determining the optimal speed ratio for the CVT includesdetermining a position for a shift rod of the CVT. In some embodiments,determining the optimum speed ratio for the CVT includes determining anumber of encoder counts for actuating a shifter mechanism of the CVT,which shifter mechanism can be a shift rod.

Referencing FIG. 31 now, an embodiment of the actuator process 2904 canstart at a state 3100 and proceed to execute an actuator control process3104. The actuator process 2904 then executes an actuator hardware anddrive module 3106. The actuator process 2904 can then end, if an actualCVT position 3108 is substantially the same as the optimum CVT positiondetermined by the shifter process 2902.

Passing to FIG. 32 now, a lookup table that can be used by the shifterprocess 2902 can be exemplified by each of the curves graphed on thechart shown. Depending on the speed of the vehicle, a speed ratio of thetransmission is selected (which is equivalently to selecting a positionof a shifting mechanism of the transmission, such a position of a shiftrod; the position can be expressed in terms of encoder counts). A curve3202 represents a lookup table for a “drag race” or fast accelerationmode. A curve 3204 represents a lookup table for an economy (“econ”)mode. A curve 3206 represents a lookup table for a fixed ratiosimulation (or “stepped”) mode. A curve 3208 represent a lookup tablefor a performance (or “hill climb”) mode. FIG. 33 is a data table usedto derive the chart of FIG. 32. MPH refers to vehicle speed; RPM refersto drive motor speed; GR refers to speed ratio of a CVT. Act Pos refersto the position of the shift rod in encoder counts.

In one embodiment, a method of controlling a drivetrain of an EVprovides for an economy mode and a performance mode. In economy mode,the control system is configured to control the drive motor in thefollowing manner. The control system allows the current to the drivemotor to have an initial maximum current peak (that is, current limit),for example 30-Amps. This initial maximum current peak can be held for apredetermined amount of time (for example 2-seconds), which amount oftime, in some cases, is preferably sufficient to allow the drive motorto achieve its base speed, said base sped being the drive motor speedabove which the motor produces constant power at increasing drive motorspeed and decreasing drive motor torque, where the drive motor typicallyoperates at higher efficiency that at lower drive motor speeds.Thereafter, the control system manages current to the drive motor suchthat current is delivered to the drive motor only up to a predeterminedcurrent limit (for example, 25-Amps), which can be sustained as long asrequired by, for example, throttle command (or user input). In someembodiments, the power (or current) supplied to the electric drive motoris a function of throttle position and battery voltage. In economy mode,the control system is configured to control the CVT in a fashion thatallows the electric motor to arrive at its base speed as quickly aspossible, and then the control system controls the CVT to maintain theCVT at a transmission speed ratio of peak efficiency for the givenoperating conditions (for example, in certain CVTs the peak efficiencyis found at a transmission speed ratio of 1:1).

In performance mode, the control system is configured to allow the drivemotor to achieve a predetermined initial maximum current limit (forexample, 60-Amps). This initial maximum current limit can be sustainedfor a predetermined amount of time (for example, 5-seconds), which canbe determined, at least in part, by considerations of circuitrytemperature specifications, circuitry life cycle, etc. Under thiscontrol strategy, the EV drivetrain is provided with high power atvehicle launch. The control system then controls the CVT in a manner toproduce high acceleration and achieve the maximum speed of the EV in ashort period. The control system, in performance mode, can be configuredso that after the initial maximum current limit has been provided, thedrivetrain can be provided with up to a predetermined maximum currentlimit (for example, 45-Amps).

In some embodiments, in either or both of the performance and economymodes, the control system can be provided with a timed linear ramp tomaximum throttle function, which can be used to ensure that the EVlaunches smoothly, rather than abruptly and to the point that it cantend to lift the front of the EV off the ground. The timed linear rampto maximum throttle function can also be used to manage power deliveryto the drive motor under various operating conditions (for example,reducing current draw during operation in economy mode).

In one embodiment, the control system is configured to optimize theoverall efficiency of the drivetrain of the EV. The drivetrain overallefficiency is a function of the efficiency of the drive motor, theefficiency of the CVT, the efficiency of the control system itself,and/or an indication of how battery life is affected at certainoperating conditions. Hence, in some embodiments, the control system isconfigured to modulate power (or current) to the electric motor and tomodulate the transmission speed ratio of the CVT (preferably inconjunction with the power modulation) based upon certain inputs, whichcan include one or more of the following: throttle position, throttleposition rate of change (with respect to time), control system mode (forexample, economy, performance, manual, simulation of steppedtransmission, etc.), average or instantaneous battery voltage, averageor instantaneous state of charge of the battery, data indicative ofbattery life versus current draw over time, average or instantaneousdrive motor current draw, average or instantaneous speed of the vehicle,transmission speed ratio of the CVT, data indicative of the efficiencyof the CVT versus speed of the EV and/or transmission speed ratio, speedof the drive motor, data indicative of the efficiency of the drive motorversus torque and/or speed of the drive motor, and efficiency of thecontrol system (such as data indicative of power use by the controlcircuitry for the shift actuator and/or the drive motor). In certainembodiments, the control system is configured to control thetransmission speed ratio of the CVT as a function of one or more of thespeed of the EV, speed of the electric drive motor, battery voltage, andcurrent draw (that is current provided to the drive motor, which can insome cases be based on throttle position).

Referencing FIG. 34 now, a bicycle rear wheel hub incorporates acontinuously variable transmission (CVT) 4700. A CVT 4700 and equivalentvariants thereof may be used in applications other than bicycles,including but not limited to, other human powered vehicles, lightelectrical vehicles, hybrid human-, electric-, or internal combustionpowered vehicles, industrial equipment, wind turbines, etc. Anytechnical application that requires modulation of mechanical powertransfer between an input source and an output load can implementembodiments of a CVT 4700 in its power train. Embodiments of the CVT4700, and related CVTs, are described in U.S. application Ser. No.11/543,311, filed Oct. 3, 2006, and entitled “Continuously VariableTransmission,” the disclosure of which is explicitly hereby incorporatedherein by reference in its entirety.

As illustrated in FIG. 34, the CVT 4700 includes a shell or hub shell4702 that couples to a cover or hub cover 4704. The hub shell 4702 andthe hub cover 4704 form a housing that, among other things, functions toenclose most of the components of the CVT 4700. A main shaft or mainaxle 4706 provides axial and radial positioning and support for othercomponents of the CVT 4700. The CVT 4700 can include a variatorsubassembly 4708 as shown in detail view C, and a shift rod and/orshifter interface subassembly 4716 as shown in detail view G.

Referencing FIG. 35, the shifter interface 4716 serves, among otherthings, to cooperate with a shifting mechanism (such as the controlsystems, including shift actuator motor, described above) to actuate theshift rod 4816 for changing the speed ratio of the CVT 4700. The shifterinterface 4716 also serves to retain the shift rod 4816 and constrainthe axial displacement of the shift rod 4816. In the embodimentillustrated, the shifter interface 4716 includes a shift rod retainernut 6502 adapted to receive the shift rod 4816 and to mount about themain axle 4706. The shifter interface 4716 may also include a nut 6504adapted to be threaded on the shift rod retainer nut 6502 for, amongother things, coupling the main axle 4706 to a dropout (not shown) of abicycle and to prevent the shift rod retainer nut 6502 from unthreadingoff the main axle 4706 during operation of the shifter mechanism.

Referring now to FIG. 36, in one embodiment the variator subassembly4708 includes a number of traction power rollers 4802 placed in contactwith an input traction ring 4810, and output traction ring 4812, and asupport member or idler 4814. A shift rod 4816 threads into a shift rodnut 4818, which is located between and is adapted to interact with shiftcams 4820. An idler bushing 4832 is piloted by the main axle 4706 andinterfaces with the shift rod nut 4818. A shift rod nut collar 4819 ismounted coaxially about the main axle 4706 and is positioned between theshift cams 4820. The shift cams 4820 contact the cam rollers 4822. Eachof several legs 4824 couples on one end to a cam roller 4822. Anotherend of each leg 4824 couples to a power roller axle 4826, which providesa tiltable axis of rotation for the power roller 4802.

Referring now to FIG. 40, in one embodiment a controller 5001 caninclude a controller housing 5006 having a set of drive cables 5002 anda set of power source cables 5003. The drive cables 5002 can beconfigured to connect electrically the controller 5001 to a drive motor.The power source cables 5003 can be configured to connect electricallythe controller 5001 to a power source, such as a battery. In someembodiments, the drive cables 5002 and power source cables 5003 are10AWG wire. The controller 5001 can further include an actuatorconnector 5004, which can be configured to connect to a mating connectorof a mechanical actuator, said mechanical actuator configured to adjusta transmission speed ratio of a CVT. The controller 5001 can be providedwith a communication port 5005 (for example, a USB port) that canfacilitate communication between the controller 5001 and a computer, forexample, or any other data or programming input or output device. Adisplay connector 5014 can be provided to facilitate the electricalcommunication of user commands, such as a desired operating mode,between the controller 5001 and a user interface. In one embodiment, thecontroller 5001 includes a throttle-brake-charger connector 5015 that isconfigured to connect to various sensors on a vehicle such as a throttlesensor, a brake sensor, and/or a charger sensor. In some embodiments,the controller 5001 can also include a serial communication port 5016.The serial communication port 5016 can be configured to allowprogramming of the controller 5001 using a process, for example,commonly known as flashing. The serial communication port 5016 istypically provided for prototype and development purposes. In oneembodiment, the actuator connector 5004, the communication port 5005,the display connector 5014, the throttle-brake-charger connector 5015,and the serial communication port 5016 are arranged on one side of thecontroller housing 5006. In some embodiments, the controller housing5006 can be a generally rectangular-shaped, sheet metal enclosure havingan interior cavity, which can be filled with a potting 5007. The potting5007 can be a plastic or resin material.

Turning now to FIGS. 41 and 42, in one embodiment, the controller 5001includes a controller board assembly 5008 that can be housed in thecontroller housing 5006 and enclosed with the potting 5007. Thecontroller board assembly 5008 can be attached to the controller housing5006. In one embodiment, the drive cables 5002, the power source cables5003, the actuator connector 5004, the communication port 5005, thedisplay connector 5014, the throttle-brake-charger connector 5015, andthe serial communication port 5016 couple to the controller boardassembly 5008. The potting 5007 can be arranged to expose theaforementioned connections while enclosing a substantial portion of thecontroller board assembly 5008. In some embodiments, a number of thermalpads 5009 are placed between the controller board assembly 5008 and thecontroller housing 5006. The thermal pads 5009 can be located on anumber of controller body protrusions 5010. The controller bodyprotrusions 5010 can be formed on the interior cavity of the controllerhousing 5006.

Passing now to FIG. 43, in one embodiment the controller board assembly5008 can include a motor control board 5011 and a transmission controlboard 5012. The motor control board 5011 preferably includes electricalcircuitry (that is, integrated electrical circuits, memory circuits,firmware, etc.) configured to facilitate control of a drive motor. Thetransmission control board 5012 preferably includes electrical circuitry(that is, integrated electrical circuits, memory circuits, firmware,etc.) configured to facilitate control of a transmission, such as a CVT,A crossover connector 5013 can be provided to electrically connect themotor control board 5011 to the transmission control board 5012. In someembodiments, the motor control board 5011 and the transmission controlboard 5012 are assembled so that the motor control board 5011 is belowthe transmission control board 5012 in the controller housing 5006. Thecrossover connector 5013 can include a female connection body 5013A anda male connection body 5013B. The female connection body 5013A can beattached to the motor control board 5011. The male connection body 5013Bcan be attached to the transmission control board 5012. During assembly,the female connection body 5013A is aligned with the male connectionbody 5013B to facilitate electrical communication between the motorcontrol board 5011 and the transmission control board 5012. In someembodiments, the control board 5011 can be disabled so that thecontroller 5001 can be used with a separate drive motor controlleralready provided with an EV. In such cases, the control board 5011 isnot employed, and the transmission control board 5012 is configured tocommunicate with the separate drive motor controller.

The foregoing description details certain preferred embodiments of thepresent invention and describes the best mode contemplated. It will beappreciated, however, that no matter how detailed the foregoing appearsin text, the invention can be practiced in many ways. The scope of thepresent invention should therefore be construed in accordance with theappended claims and any equivalents thereof.

What is claimed is:
 1. A drive system comprising: a drive motor; a motorcontroller communicatively coupled to the drive motor; a continuouslyvariable transmission (CVT) having a plurality of tiltable sphericalplanets arranged radially about a longitudinal axis of the CVT; atransmission control system coupled to the CVT, the transmission controlsystem comprising a controller configured to be in electricalcommunication with an actuator configured to adjust an angle of thetiltable spherical planets, the controller configured to control theactuator to change a speed ratio of the CVT, a first sensor configuredto provide vehicle speed data, a second sensor configured to providedata associated with the transmission speed ratio of the CVT, and athird sensor configured to provide data associated with a batteryvoltage; and a data display in electrical communication with thecontroller, the data display having at least one button for selectingfrom a plurality of operating modes.
 2. The drive system of claim 1,wherein the CVT is enclosed in a housing integrated into a wheel of anelectric vehicle.
 3. The drive system of claim 2, wherein the housing isadapted to cooperate with the actuator, and wherein the actuator isconfigured to adjust an angle of the tiltable spherical planets based atleast in part on one of the plurality of operating modes and on anindication of transmission speed ratio of the CVT.
 4. The drive systemof claim 1, wherein the second sensor comprises an actuator positionsensor.
 5. The drive system of claim 1, wherein the controller isconfigured to control the actuator based at least in part on dataindicative of a transmission speed ratio and a vehicle speed.
 6. Thedrive system of claim 1, wherein the motor controller is integrated withthe transmission control system.
 7. The drive system of claim 1, furthercomprising a sensor configured to provide data associated with a currentlevel provided to the drive motor.